First Year Laboratory: Project Proposal

FIRST YEAR LABORATORY: PROJECT PROPOSAL - 2006

PROJECT TITLE CODE ASTR06 GALAXY TWO-POINT CORRELATION FUNCTION DEMONSTRATOR TELEPHONE RESEARCH Davide Rizzo NUMBER GROUP 7594 1965 Astrophysics E-MAIL ADDRESS ROOM NUMBER [email protected] 1003

PROJECT OUTLINE: The aim of this project is to develop a C++ program to compute the two- point correlation function for a simulated catalogue of galaxies. It is well known that one of the problems cosmologists had to face in the past is to explain how the Universe has evolved from a highly homogeneous initial state to the inhomogeneus actual state, where matter has condensed to form stars, galaxies and clusters of galaxies. We won’t go into details about which theories were proposed and how well they explain observations. Let’s just imagine we have a large catalogue of galaxies for a region of sky. For each galaxy we have its coordinates and can thus plot its position on a map. How can we tell if, and to what extent, this map differs from a bunch of points randomly scattered on the same area? The two-point correlation function solves this problem. It can be loosely defined as a function of one variable (the angular distance) giving the probability that two galaxies are separated by that particular distance. It can be thought of as a lumpiness factor - the higher the value for some distance scale, the more lumpy the Universe is at that distance scale. Various formulas, or estimators, exist to compute this quantity, all of which need a comparison random catalogue. Therefore the first task will be to develop a function to provide such a catalogue. The simulated galaxy catalogue will be obtained from the GalICS website (http://galics.iap.fr). GalICS stands for Galaxies In Cosmological Simulations and allow to obtain catalogues of objects from detailed cosmological simulations. Our code will then be applied to the catalogue to investigate for deviations from randomness at various angular scales. We will also test the different estimators on a random catalogue. The correlation scale should be zero at all scales for such a catalogue: we will verify that this is indeed the case. Please note that a three-point correlation function also exists, taking into account the line of sight distances of the galaxies (measured by redshift) in addition to their position on the celestial sphere. In this project we’ll just deal with the two points function.

This project is available on: Thursday/Friday Code: PROJECT ASSESSMENT SHEET – 2006 Leave blank

Are there any safety aspects which need special attention (i.e. use of lasers, radioactive sources)? NO

Is this a computing project? YES If it is would it be done on: [a] The PC network [b] Computing facilities within your research group If the answer to [a] was yes then complete the following three questions: [i] Do you require additional software or libraries? NO [ii] Do you anticipate exceptional cpu or disk storage (>100Mbyte) requirements? NO [iii] Have you discussed your requirements with Martin Morris? YES Which programming language are you wishing to use? C++ Are you proficient in the necessary programming language? YES